CODEWITHSUNDEEP
javamysqlhibernatejakarta-eeentity-relationship
Thusitha Niroshan
Thusitha Niroshan

Reputation: 303

One to many table creation

I'm really new to Hibernate and this is my first app which is enterprise level. I'm stuck at one to many mapping. I did the mapping whole day but it doesn't give to correct table structure for me.

Here is the ER diagram I want to map ER Diagram

These are the Classes

Feed Class

@Entity
public class Feed {

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private long id;
private String name;
private long quantity;
//With getters and setters
}

Feed Order Details Class

@Entity
public class FeedOrderDetail {

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private Long id;
private double unitPrice;
private long quantity;

@OneToMany(cascade=CascadeType.MERGE)
@JoinColumn(name="feed_id")
private List<Feed> feed = new ArrayList<Feed>();

//Getters and Setters
}

after deploying app I get the following table structure

Table Structure

My problems are why feed_id is in Feed table? Should I add same feed every time I add a feed order detail? (it isn't a good idea)

I can achieve this by moving @OneToMany annotation and attributes to Feed table. but if I move it to Feed class how can I represent feed order details in JSP pages?

I'm using spring with this project also.

Upvotes: 2

Views: 82

Answers (4)

slartidan
slartidan

Reputation: 21576

I would suggest to have a object reference on both sides of the relationship.

So have a reference to List<FeedOrderDetail> in Feed and have a single refernce to a Feed in your FeedOrderDetail.

Class Feed:

@Entity
public class Feed {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private long id;
    private String name;
    private long quantity;
    //With getters and setters

    // !new!
    @OneToMany(mappedBy = "feed") // mappedBy references the fieldname in the other Java class
    private List<FeedOrderDetail> details;
}

Class Detail:

@Entity
public class FeedOrderDetail {

     @Id
     @GeneratedValue(strategy=GenerationType.AUTO)
     private Long id;
     private double unitPrice;
     private long quantity;

     @ManyToOne(cascade=CascadeType.MERGE)
     @JoinColumn(name="feed_id")
     private Feed feed; // only a single feed reference

     //Getters and Setters
}

If you want to get a list of feeds using Hibernate's JPA API, then you can use this code:

TypedQuery<Feed> query = entityManager.createQuery("SELECT f FROM Feed f", Feed.class);
List<Feed> feeds = query.getResultList();

Upvotes: 1

Vishal Zanzrukia
Vishal Zanzrukia

Reputation: 4973

My problems are why feed_id is in Feed table?

You are right, it should not be in case your ER diagram is right.

Your ER diagram and table structure does not match, so I am trying to give you class mapping according to your ER-diagram.

Feed.java

@Entity
public class Feed {

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private long id;
private String name;
private long quantity;
//With getters and setters
@OneToMany(fetch = FetchType.LAZY, mappedBy = "feed")
    public Set<FeedOrderDetail> getFeedOrderDetail() {
        return this.feedOrderDetail ;
    }
}

FeedOrderDetail.java

@Entity
public class FeedOrderDetail {

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private Long id;
private double unitPrice;
private long quantity;

@ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "FEED_ID", nullable = false)
    public Feed getFeed() {
        return this.feed;
    }

//Getters and Setters
}

I hope it helps :)

Upvotes: 0

ap0calypt1c
ap0calypt1c

Reputation: 481

The correct one is:

@Entity
public class Feed {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private long id;
private String name;
private long quantity;
//With getters and setters
@OneToMany(cascade=CascadeType.MERGE, mappedBy="feed")
private List<FeedOrderDetail> orders = new ArrayList();
}

And 

@Entity
public class FeedOrderDetail {

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private Long id;
private double unitPrice;
private long quantity;

@ManyToOne(cascade=CascadeType.MERGE)
@JoinColumn(name="feed_id")
private Feed feed;

//Getters and Setters
}

Upvotes: 0

JB Nizet
JB Nizet

Reputation: 691735

You designed it backwards. You schema says that 1 Feed instance includes M FeedOrderDetail instances.

So, in the class Feed, you should have a List<FeedOrderDetail>. But that's not what you've done. You have a List<Feed> in FeedOrderDetail.

Upvotes: 1

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